Necropsies reveal how six of the 12 North Atlantic right whales that died in Canadian waters this summer met their end.

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After two months studying the carcasses of seven right whales found dead off Canada’s Atlantic coast this past summer, scientists have revealed what killed six of the endangered animals.

On October 5, Pierre-Yves Daoust, a pathologist at Prince Edward Island’s Atlantic Veterinary College, and Émilie L. Couture, a veterinarian at Zoo de Granby and Université de Montréal, released the results of their investigation into the unprecedented mortality event of this beleaguered species.

There was no evidence of biotoxins. No suggestion of infectious diseases. In fact, the findings were entirely predictable: internal bleeding suggested that four of the necropsied whales had died from blunt trauma, aka from collisions with ships. (Nothing else in the ocean is big and fast enough to do that kind of damage to a 65-tonne whale.) Two others had died from entanglement in snow crab fishing gear, though nearly all the carcasses had scars consistent with entanglement. The scarring was no surprise—as the report’s authors noted, 83 percent of right whales are entangled in fishing gear at some point in their lives. The seventh whale was so severely decomposed that the cause of death could not be determined.

Nearly all the whales examined had died as a result of human activity. As one of the report’s coauthors, Tonya Wimmer of Nova Scotia’s Marine Animal Response Society, says, “That’s not new information.”

Researchers have known for some time that vessel strikes and entanglement are the two main causes of deaths in North Atlantic right whales, throughout their range. Aside from the whales that died, another five live whales were entangled in fishing gear in the Gulf of St. Lawrence this summer. In July, New Brunswick fisherman Joe Howlett died disentangling one of them.

Dubbed the urban whale, the North Atlantic right whale has a predilection for hanging out in areas that are busy with human activity—it migrates up and down the east coast of Canada and the United States, an area choked with shipping lanes and fishing gear. But this summer, researchers were surprised to find about a quarter of the population in the Gulf of St. Lawrence. The summer right whale hotspot appears to be a relatively new phenomenon. No one but the whales, however, knows this for sure, because the Gulf has not been a focus of right whale research until quite recently.

Being a new (or at least newly discovered) hangout for right whales, the Gulf of St. Lawrence was also a more dangerous one. Shipping and fishing practices had not been modified to accommodate for the whales’ presence as they had been in other areas where whales and marine traffic overlap. But the report validates the measures that Transport Canada and Fisheries and Oceans Canada (DFO) quickly put into place this summer. These included voluntary and then mandatory speed reductions for ships in critical areas as well as early closure of snow crab fisheries and a concerted effort to recover gear that had been lost or left behind.

Even so, 15 North Atlantic right whales have been confirmed dead in 2017 (12 in Canada and three in the United States), out of a dwindling population now estimated at 458. There has not been a mortality event of this proportion since the days of whaling. Daoust’s team had set a record, performing seven necropsies in two months. “A record we should not be happy about,” he says.

Surviving right whales will be leaving the Gulf of St. Lawrence soon, as they begin to migrate south to warmer waters for the winter. The government’s focus is now on what will happen next spring if the whales return to this busy corner of Canada’s coast. New measures must ensure this kind of die-off won’t happen again.

This is easier said than done. The Gulf of St. Lawrence is Canada’s major shipping corridor and approximately CAN $7-billion in direct Canadian trade flowed through the region in the last year. Moreover, the southern Gulf alone accounts for 15 percent of the total catch value of Canadian fisheries. Jane Weldon, director general of Marine Safety and Security at Transport Canada, says her department will take its lead from the scientists at DFO. If the animals change their migratory patterns again, her ministry will consider designating other slow zones. Meanwhile, DFO is holding meetings with stakeholders in the fishing industry.

There will be plenty for the North Atlantic Right Whale Consortium to talk about when it gathers for its annual meeting in Halifax, Nova Scotia, later this month.

Meanwhile, the 2016 proposed action plan for the North Atlantic right whale, which aims to reduce injury and mortality from entanglement in fishing gear, still hasn’t been presented to Dominic LeBlanc, Minister of Fisheries, Oceans, and the Canadian Coast Guard for his signature. After the events of the summer, the department says it must now be revised before it will be signed.